What is a phantom read?

Can you explain what a phantom read is?

Sure! A phantom read occurs when a transaction reads a set of rows that match a certain condition, but another transaction inserts or deletes rows that affect that condition before the first transaction is completed.

How does it differ from dirty reads and non-repeatable reads?

Great question! Dirty reads allow a transaction to read uncommitted changes from another transaction, while non-repeatable reads occur when a row is changed by another transaction after it has been read. Phantom reads specifically involve changes to the set of rows that match a query.

What are the implications of phantom reads in database systems?

Phantom reads can lead to inconsistent results and can affect the integrity of data. To prevent them, database systems often use isolation levels like Serializable.

Can you give an example of a scenario where a phantom read might occur?

Certainly! Imagine a bank database where one transaction reads all accounts with a balance over $1000. If another transaction adds a new account with a $1500 balance before the first transaction completes, the first transaction might not see that new account, leading to a phantom read.